1. Field of the Invention
Lightweight units especially suited for housing electronic components capable of handling relatively large electrical loads desirably are cast of aluminum so that cooling fins may be made an integral part of the unit. The provision of reinforcing ribs, cooling fins and other internal or external integral protrusions dictates use of sand casting procedures in manufacture of housings of this general type for cost and structural integrity purposes. Furthermore, these units which may for example have width, height and length dimensions of the order of two or three feet or more. As a result, and in view of the desirability of sand casting fabrication, 356 aluminum alloy is generally used for such purposes.
In instances where the sand cast 356 aluminum alloy housing is used for electronic or electrical components which generate heat, it is conventional to provide a cooling medium within the interior of the housing and often comprising a fluid such as freon or the like under pressure. When excessive heat is generated in the interior of the housing, it is necessary to relieve such pressure in order to prevent catastrophic rupture of the 356 sand cast aluminum alloy housing. Efforts to provide relief valves have not heretofore been entirely successful. On the other hand though, incorporation of rupture discs in vent openings in the 356 aluminum alloy sand cast housing units has not been successfully accomplished because of the difficulty of securing the rupture disc in a relief vent in the housing without adverse effects on the physical properties of the rupture disc and particularly the burst pressure thereof.
The pressure relief cannot be provided by utilization of a rupture disc carried by a tubular assembly which is simply threaded into an opening therefor in the housing because of the fact that such threaded connection does not provide a truly hermetic seal which assures retention of the cooling medium in the housing. Relief valves suffer from the same disability. Therefore, a true hermetic seal can be provided only be welding of the rupture disc assembly to the housing unit.
2. Description of the Prior Art
Efforts to weld rupture disc assemblies to 356 aluminum alloy, heat-treated, sand cast units such as housings for electronic or electrical components which dissipate heat and therefore require a cooling medium in surrounding relationship thereto, have heretofore been frustrated by the fact that impurities in the outer surface of the cast housing resulting from residual deposits of sand and other foreign matter have precluded welding of a rupture disc support to the body of the housing. In order to overcome the effect of the impurities at the surface of the cast body where welding was attempted, it was found necessary to introduce so much heat to the parts that damage occurred to the support for the disc and particularly the rupture disc itself, thus altering its burst characteristics and preventing provision of a disc that would reliably open at a pre-established pressure level.
When attempts were made to solve this problem by heat sinks or the like, then the integrity of the weld deteriorated to a point where a true hermetic seal was impossible to obtain.